Hitherto flue gas desulfurization processes based on the spray drying-absorption-principle have primarily been performed using slaked lime as absorbent, and by using recycling of the absorbent and careful control of various parameters in the process it is possible to obtain a rather efficient utilization of said absorbent in the process.
However, in large plants such as power stations the absorbent costs are considerable and, especially in case of high sulfur coal, may represent a bar to the utilization of the otherwise very attractive spray drying-absorption desulfurization.
Therefore it is an object of the present invention to minimize absorbent costs in the spray drying-absorption desulfurization.
Said object and other advantages are obtained by the process according to the invention which makes possible an efficient utilization of an absorbent which is considerably cheaper than slaked lime, viz. limestone. Alternatively the process may be performed using e.g. slaked lime obtaining a substantially more efficient utilization thereof than in the prior art spray drying-absorption processes.
Use of limestone (CaC0.sub.3, MgC0.sub.3 and other naturally occuring impurities) as absorbent in flue gas desulfurization processes is well known in connection with wet scrubbing.
However, in the spray drying-absorption processes limestone has hitherto been regarded as unsuitable because only a very small proportion of the limestone introduced in these prior art processes reacts with the sulfur oxides in the waste gas and therefore no economical benefits were obtained by using limestone, even if said material is 5-10 times cheaper than slaked lime.
Known is also a gas desulfurization process in which a partial desulfurization takes place by passing the gas through of fluidized bed of particles of solid absorbent which is preferably CaO or precursors therefore (cf. Moss U.S. Pat. No. 4.081.513). The thus partly desulfurized gas is afterwards cleaned by means of a wet scrubbing process and the sludge resulting therefrom dried in said fluidized bed. However, the operation of such a combined system is complicated and is less suitable than the spray drying-absorption process for treating large amounts of waste gas.